The present invention relates to an ammonia recovery device and to a recovery method, with which ammonia is recovered together with CO2 and H2S from an ammonia-containing wastewater from a gasification furnace, such as a coal gasification furnace, using a fossil fuel as a raw material, whereby the purified wastewater is usable as industrial water.
Wastewaters from gasification furnaces, such as coal gasification furnaces, which use a fossil fuel as a raw material, contain ammonia (NH3) as well as CO2, H2S, and the like. Accordingly, in general, an ammonia stripper is operated under atmospheric pressure to release NH3, CO2, and H2S contained in the wastewaters while water that is reusable as industrial water is recovered from a tower bottom of the ammonia stripper.
H form of a conventional device for recovering ammonia from such a wastewater as described above is shown in FIG. 3. In FIG. 3, an ammonia stripper 301 is operated under atmospheric pressure, and an ammonia-containing wastewater (also containing CO2 and H2S) is introduced through a wastewater supply pipe 302 into this ammonia stripper 301.
The ammonia stripper 301 is maintained at a pressure, measured by a pressure gauge 303, of atmospheric pressure and at a temperature, measured by a thermometer 304, of approximately 90° C. In this case, NH3, CO2, H2S, and water (H2O) are released from the ammonia-containing wastewater; therefore, NH3, H2S, and CO2 gases are discharged from a tower top 305. These NH3, H2S, and CO2 gases are to be served for burning. Furthermore, a wastewater from a tower bottom 306 of the ammonia stripper 301 is used as industrial water.
It should be noted that the NH3 and H2S gases change as follows:NH3→N2+H2OH2S→SO2+H2O
Furthermore, in FIG. 4, another form of a conventional device for recovering ammonia from a wastewater is shown. Note that this form is suggested in the paragraph [0003] of JP 2004-67849 A.
In FIG. 4, an ammonia stripper 401 is generally operated under normal pressure (atmospheric pressure), and an ammonia-containing wastewater (also containing CO2 and H2S) is introduced through a wastewater supply pipe 402 into the ammonia stripper 401. At this time, NaOH is supplied to the wastewater supply pipe 402 from a NaOH supply pipe 407 so that NaOH can be injected into the ammonia-containing wastewater.
The ammonia stripper 401 is maintained at a pressure, measured by a pressure gauge 403, of normal pressure (atmospheric pressure) and a temperature, measured by a thermometer 404, of approximately 90° C. In this case, NH3 and water (H2O) are released from the ammonia-containing wastewater containing NaOH; therefore, NH3 and water (H2O) are discharged from a tower top 405 in the form of an ammonia vapor product.
With the supply of NaOH, the following reactions occur.NaOH+H2S→NaSH+H2O2NaOH+CO2→Na2CO3+H2O
As a result, NaOH, Na2CO3, NaSH, and water (H2O) are discharged from a tower bottom 406, and then transferred for wastewater treatment.
However, the above-described techniques both have their own drawbacks as follows.
The device for recovering ammonia from a wastewater shown in FIG. 3 has the following problems.
(1) NH3 together with CO2, H2S, water (H2O), and the like discharged from the tower top 305 of the ammonia stripper 301 are burned in an incinerator, and then subjected to flue gas desulfurization. Accordingly, ammonia (NH3) cannot be recovered.
(2) In addition, for the purposes of efficiently releasing ammonia and preventing precipitation of ammonium carbonate, the outlet temperature (the thermometer 304) of the ammonia stripper 301 needs to be maintained at approximately 90° C. This results in an increase in the amount of moisture contained in the gas. Accordingly, although sulfur can be recovered in the form of gypsum during the desulfurization, there arise problems in that the cost increases or in that only dilute sulfuric acid can be recovered, since water separation is essential for a gas used as a raw material gas for production of highly concentrated sulfuric acid (98 wt %).
In addition, the form of the device for recovering ammonia from a wastewater as shown in FIG. 4 has the following problems.
(1) In order to recover ammonia, it is possible to recover a gas rich in NH3 from the tower top 405 by supplying NaOH through the NaOH supply pipe 407 to be mixed into an ammonia-containing wastewater so as to fix CO2 and H2S by the action of NaOH. However, in such a case, the amount of NaOH to be used is enormous (for example, at a commercial scale of 1000-fold expansion of the laboratory base shown in Table 1, it would be approximately 35 tons per day).
(2) In addition, without the supply of NaOH, water with a quality approximately equivalent to that of industrial water can be obtained from the tower bottom 406 of the ammonia stripper 401. However, when NaOH is added to this water, such a quality that is approximately equivalent to that of industrial water cannot be maintained. Accordingly, thus obtained water needs to be sent to a wastewater treatment facility for treatment to restore a quality approximately equivalent to that of industrial water.